Surface Loading Rate Research Articles

Effects of substrate loading rate on biofilm structure

The effects of substrate surface loading rate on biofilm growth and structure were investigated by chemical, biochemical and microscopic methods. Three tubular reactors were operated at equal C:N ratio of 0.1, with substrate loading rates of 1.2, 0.6 and 0.3 g-C/m 2/day. Substrate loading positively influenced the biofilm growth rate. Denser biofilms with lower porosities were formed at higher substrate loading. Slowly growing biofilms having porous structures were found to have higher specific activities. Nitrification was suppressed under the higher substrate loading conditions even at the equal C:N ratio of 0.1, thus proving that the spatial competition between nitrifiers and heterotrophs as one limiting criteria for stable nitrification. The spatial organization of the ammonia oxidizers was biofilm structure related. The strain variability of ammonia oxidizers was substrate loading dependent. These findings suggest that substrate loading is a key parameter in determining biofilm structure and function.

Effects of substrate loading rate on biofilm structure

The effects of substrate surface loading rate on biofilm growth and structure were investigated by chemical, biochemical and microscopic methods. Three tubular reactors were operated at equal C:N ratio of 0.1, with substrate loading rates of 1.2, 0.6 and 0.3 g-C/m2/day. Substrate loading positively influenced the biofilm growth rate. Denser biofilms with lower porosities were formed at higher substrate loading. Slowly growing biofilms having porous structures were found to have higher specific activities. Nitrification was suppressed under the higher substrate loading conditions even at the equal C:N ratio of 0.1, thus proving that the spatial competition between nitrifiers and heterotrophs as one limiting criteria for stable nitrification. The spatial organization of the ammonia oxidizers was biofilm structure related. The strain variability of ammonia oxidizers was substrate loading dependent. These findings suggest that substrate loading is a key parameter in determining biofilm structure and function.

Dermal exposure to dry powder spray paints using PXRF and the method of Dirichlet tesselations.

This paper describes workplace dermal exposure measurements that were carried out by the Health and Safety Laboratory as part of the EU RISKOFDERM project to measure dust contamination. Exposure to dry powder spray paints was measured at five sites on 12 subjects. Twenty-two samples were obtained, of which eight contained triglycidyl isocyanurate (TGIC) and 14 did not. All subjects wore Tyvek whole body oversuits and some wore sampling gloves. These were either analysed in their entirety to extract the TGIC or surface scanned over representative areas using a portable X-ray fluorescence spectrometer (PXRF) to detect barium or titanium in the fillers of the paints. The method of Dirichlet tessellation was used to map the scans and the technique was developed further for these studies to extend measurements to gloves and to take limits of detection into consideration. The PXRF allowed dusts to be measured in situ that would otherwise be difficult to extract from the material and analyse by other means. The geometric mean surface loading rate of the 22 oversuits was 43 micro g/cm/(2)/h (GSD = 6.0) and of the 23 pairs of sampling gloves was 970 micro g/cm(2)/h (GSD = 8.6). Exposure patterns could be attributed to the arrangements of the subjects, spray booths and the workpieces. Similar exposures were found for TGIC and titanium fillers in factories with similar methods of ventilation.

Dermal exposure to electroplating fluids and metalworking fluids in the UK.

This paper describes workplace dermal exposure measurements that were carried out by the Health and Safety Laboratory as part of the EU RISKOFDERM project. Exposure to metalworking fluids (MWFs) was measured at three sites on 25 subjects who were 'mechanically treating solid objects' as they loaded and supervised milling and boring machines and lathes. Thirty-one samples were obtained, of which 18 were exposures to neat mineral oils and 13 to water-oil mixes. All subjects wore Tyvek whole-body oversuits that were analysed in their entirety to extract the MWF. The geometric mean surface loading rate of the 31 oversuits was 62 micro g/cm(2)/h (GSD = 4.6) and of the seven pairs of sampling gloves (worn inside protective gloves) was 2900 micro g/cm(2)/h (GSD = 1.67). Exposure to electroplating fluids was measured at three sites on 27 subjects who were dipping objects into tanks of either chromic acid, nickel sulphate, copper sulphate, copper cyanide or zinc hydroxide. All subjects wore Tyvek whole-body oversuits that were surface scanned over their areas using a portable X-ray fluorescence spectrometer to detect all the metal atoms simultaneously. Contamination was assessed using the method of Dirichlet tessellation. The geometric mean surface loading rate of the 26 oversuits was 37 micro g/cm(2)/h (GSD = 3.5) and of the 25 pairs of sampling gloves (worn inside protective gloves) was 190 micro g/cm(2)/h (GSD = 2.75). Almost all of the electroplating samples were below the limit of quantification. More than one species of metal atoms was found on some of the samples afterwards, indicating cross-contamination from other baths during the sampling period.

Adsorption Characteristics of Oxide Coated Buoyant Media (ρs<1.0) for Storm Water Treatment. I: Batch Equilibria and Kinetics

Urban rainfall-runoff mobilizes and transports significant loads of metal species. Promulgation of National Pollutant Discharge Elimination System Phase II regulations has spurred development of Unit Operations and Processes (UOPs) Best Management Practices (BMPs) for control of metal species. Recent UOP designs provide both adsorption and filtration using engineered media such as manganese oxide coated polymeric media (MOPM). Divalent metal species adsorption onto a manganese oxide coated polymeric medium was evaluated through batch adsorption experiments using a flowthrough batch reactor. Freundlich isotherms were utilized to fit the experiment data. For the media examined, MOPM, adsorption is pH dependent and results indicate a favorable solute pH range of >6 for metal species adsorption. The relative adsorption affinity of MOPM for four divalent metal species typically found in storm water is Pb(II)>Cu(II)>Cd(II)>Zn(II). Adsorption rates were rapid for this flowthrough batch system with over 50% removal in the first 30 min and over 90% removal within 5 h at a surface loading rate of 500 mL/cm2 min. The pH drift patterns, due to surface complexation, during each experiment, coincided with the metal species removal rate curve. Study results indicated that the inclusion of a thin manganese coating can significantly increase media adsorption capacity. MOPM has a comparable adsorption capacity for the divalent metal species compared to other commercial and research media.

Estimating contaminant dose for intermittent dermal contact: model development, testing, and application.

Assessments of aggregate exposure to pesticides and other surface contamination in residential environments are often driven by assumptions about dermal contacts. Accurately predicting cumulative doses from realistic skin contact scenarios requires characterization of exposure scenarios, skin surface loading and unloading rates, and contaminant movement through the epidermis. In this article we (1) develop and test a finite-difference model of contaminant transport through the epidermis; (2) develop archetypal exposure scenarios based on behavioral data to estimate characteristic loading and unloading rates; and (3) quantify 24-hour accumulation below the epidermis by applying a Monte Carlo simulation of these archetypal exposure scenarios. The numerical model, called Transient Transport through the epiDERMis (TTDERM), allows us to account for variable exposure times and time between exposures, temporal and spatial variations in skin and compound properties, and uncertainty in model parameters. Using TTDERM we investigate the use of a macro-activity parameter (cumulative contact time) for predicting daily (24-hour) integrated uptake of pesticides during complex exposure scenarios. For characteristic child behaviors and hand loading and unloading rates, we find that a power law represents the relationship between cumulative contact time and cumulative mass transport through the skin. With almost no loss of reliability, this simple relationship can be used in place of the more complex micro-activity simulations that require activity data on one- to five-minute intervals. The methods developed in this study can be used to guide dermal exposure model refinements and exposure measurement study design.

Removal of Nitrogen and Phosphorus Using Dominant Riparian Plants in a Hydroponic Culture System

The objective of the study was to evaluate potential nutrient removal capacities from eutrophic stream waters using two riparian plants, Phragmites japonica and Salix gracilistyla. The removal efficiencies, removal rates of nutrients (N, P), and their specific growth rate were estimated as a function of inflow loading rate and hydraulic retention time (HRT) in a hydroponic culture system. Weight specific growth rates (WSGR) of P. japonica increased by 0.015 d−1 in the ambient concentrations of NH4–N, NO3–N, and PO4–P and increased up to 9 times higher than the control (i.e., base concentration), whereas the WSGR decreased at the higher levels of nutrients. Under the same nutrient concentrations, the WSGR in the S. gracilistyla increased up to 9 times higher than the control, and then increased slowly. Nutrient removal efficiencies of both species were higher under lower N and P concentrations and longer HRT conditions. The removal rate of P. japonica had a positive functional relation with surface loading rates of nutrients and leveled off at 3.0 g d−1 of NH4–N, 12.5 g d−1 of NO3–N, and 3.0 g d−1 of PO4–P, respectively. The removal rate of S. gracilistyla also enhanced at the surface loading of 5 g d−1 of NH4–N, 23 g d−1 of NO3–N, and 5 g d−1 of PO4–P, respectively, but was lower than that of P. japonica. It is concluded that the nutrient removal approach using the riparian plants may be used for efficient water quality management in the eutrophic streams with long HRT.

Integrated biological and catalytic oxidation of organics/inorganics in tannery wastewater by rice husk based mesoporous activated carbon–– Bacillus sp.

The rice husk based activated carbon (RHAC), used in this study was precarbonized and activated using phosphoric acid. The activated carbon was characterized with the help of N 2-adsorption/desorption, FT-IR and scanning electron microscope to determine surface area, functional groups and surface morphology respectively. Bacillus sp. isolated from tannery wastewater was immobilized in this rice husk based activated carbon and packed in a reactor (named CAACO reactor). The wastewater having the following characteristics––chemical oxygen demand (COD): 1716 ± 392 mg/l; biological oxygen demand (BOD): 393 ± 114 mg/l, sulphate: 940 ± 217 mg/l and sulphide: 193 ± 56 mg/l––was applied at a hydraulic loading rate of 0.7376 m 3/m 3/day and surface loading rate of 0.2438 m 3/m 2/day to the CAACO reactor. The temperature was maintained at 30 °C and the pressure at one atmosphere. It was found that the reduction in COD, BOD, sulphide and sulphate were respectively 87%, 96%, 100% and 40% under an air oxidation of 2 h.

Grassed swales for stormwater pollution control during rain and snowmelt

The retention of suspended solids, particles and heavy metals in different grassed swales during rain events and snowmelt is discussed. The experimental results derived from investigations performed in existing grassed swales in the Luleå region, Northern Sweden. During high pollutant loading rates, grassed swales retain significant amounts of pollutants, mainly due to sedimentation of particulate matter. Low to moderate removal efficiencies could be expected for heavy metals, especially metals in solution (i.e. the dissolved phase). When grassed swales receive urban runoff with low pollutant concentrations, they may release rather than retain pollutants. Swales are important snow deposit areas in the city and particle bound pollutants do to a large extent remain in the swale after snowmelt. However, dissolved pollutants (i.e. dissolved heavy metals) are likely to escape the swale with the melt water. Grassed swales may be regarded as facilities that even out the peaks in pollutant loads without being capable of producing consistent high removal rates. This suggests that swales should be considered as primary treatment devices. Possible design parameters for grassed swales are mean hydraulic detention time, surface loading rate or specific swale area.

무산소-RBC 공정을 이용한 질소제거 특성 및 동력학적 인자 도출

This study was conducted to investigate anoxic-RBC (rotating biological contactor) and its application in advanced municipal wastewater treatment process to remove biologically organics and ammonia nitrogen. Effluent COD and nitrogen concentration increased as the increase of volumetric loading rate. But, the concentration changes of NO<TEX>$_2$</TEX><TEX>$\^$</TEX>-/ -N and NO<TEX>$_3$</TEX><TEX>$\^$</TEX>-/ -N were little, as compared to COD and NH<TEX>$_4$</TEX><TEX>$\^$</TEX>+/ -N. When the volumetric loading rate increased, COD removal efficiency and nitrification appeared very high as 96.7∼98.8% and 92.5∼98.8%, respectively. However, denitrification rate decreased to 76.2∼88.0%. These results showed that the change of volumetric loading rate affected to the denitrification rate more than COD removal efficiency or nitrification rate. The surface loading rates applied to RBC were 0.13～6.0lg COD/㎡-day and 0.312∼1.677g NH<TEX>$_4$</TEX><TEX>$\^$</TEX>+/-N㎡-day and they were increased as the increase of volumetric loading rate. However, the nitrification rate showed higher than 90%. The thickness of the biofilm in RBC was 0.130 ∼0.141mm and the density of biofilm was 79.62∼83.78mg/㎤. They were increased as surface loading rate increased. From batch kinetic tests, the k<TEX>$\_$</TEX>maxH/ and k<TEX>$\_$</TEX>maxN/ were obtained as 1.586 g C/g VSS-day, and 0.276 g N/g VSS-day, respectively. Kinetic constants of denitrifer in anoxic reactor, Y, k<TEX>$\_$</TEX>e/, K<TEX>$\_$</TEX>s/, and k were 0.678 mg VSS/mg N, 0.0032 day<TEX>$\^$</TEX>-1/, 29.0 mg N/l , and 0.108 day<TEX>$\^$</TEX>-l/, respectively. P and K<TEX>$\_$</TEX>s/, values of nitrification and organics removal in RBC were 0.556 g N/㎡-day and 18.71 g COD/㎡-day, respectively.

The vortex concentrator for suspended solids treatment

The use of vortex concentrators is becoming increasingly popular for suspended solids reduction in combined sewer overflows and stormwater. This study is a laboratory investigation of the use of vortex concentrators to reduce the solids concentration of synthesized stormwater. The synthesized stormwater was made with water and addition of particles; sand, granular activated carbon, and sewer sediments. The vortex concentrator was made of acryl resin 300 mm in diameter. To determine the efficiency for various influent suspended solids (SS) concentrations, tests were performed with different SS concentrations. The samples were taken simultaneously at the influent storage tank and effluent tank, and measured SS concentrations. The range of surface loading rates were 120 to 850 m3/m2/day, and influent SS concentrations were varied from 300 to 5,000 mg/L. To determine the optimum coagulant dosage, jar tests were conducted with coagulants such as PAM and PAC. It was found that optimum coagulant and its dosage were PAM and 2 mg/L. The overall SS removal efficiency of the vortex concentrator for typical stormwater was estimated at about 65%. With an increase of SS concentration, the removal efficiency was increased. Since the SS concentration of stormwater was higher than 1,000 mg/L, the removal efficiency of the vortex concentrator for stormwater could be estimated to be 65-70%. The SS removal efficiency was increased with an increase of retention time, and the optimum retention time was 0.15-1.0 minutes. With an increase of the foul to overflow Q(F)/Q(o), a key parameter for vortex concentrator operation, the removal efficiency was increased. An alternative solution to improve treatment efficiency might be to set a follow-up retention basin. Based on a series of settling tests on the treated overflow water from the vortex concentrator, 5 to 10 minutes hydraulic retention time in a follow-up retention basin would substantially improve the results.

Solvent extraction for separating micellar-solubilized contaminants and anionic surfactants.

Decontamination of contaminant-laden surfactant solutions is critical to successful implementation of surfactant-enhanced aquifer remediation (SEAR). Solvent extraction was studied for removing micellar-solubilized contaminants having low equivalent alkyl carbon numbers (EACNs) from surfactant solutions. Factors influencing the solvent extraction of micellar-solubilized contaminant were studied, including surfactant concentration, solution salinity, solvent solubilization, and solvent/solution volumetric ratio. A model was developed to quantify the impacts of these factors on contaminant removal. The good agreement between experimental results and model predictions corroborates assumptions made in the model development. From these results, it is concluded that extracting solvents must have much higher EACNs than that of the contaminant to reduce the micellar solubilization of the solvents, which can significantly reduce contaminant removal efficiency. However, the highest EACN solvent is not necessarily the best one for contaminant removal due to other constraints (e.g., molecular weight and viscosity). Increasing the total surfactant concentration or salinity of an anionic surfactant solution increases its contaminant solubilization capacity but reduces the contaminant removal efficiency by solvent extraction. Continuous column extraction operated at a low column surface loading rate allowed contaminant partitioning to approach equilibrium conditions, and multistage column extraction was able to improve the contaminant removal efficiency while minimizing solvent requirement.

Modelling the global efficiency of dissolved air flotation

The purpose of this paper is to examine how the efficiency of dissolved air flotation is affected by the size of bubbles and particles. The rise speed of bubble/particle agglomerates is modelled as a function of bubble and particle size, while the kinematics of the bubble attachment process is modelled using the population balance approach adopted by Matsui, Fukushi and Tambo. It is found that flotation, in general, is enhanced by the use of larger particles and larger bubbles. In particular, it is concluded that for the ultra-high surface loading rates of 25 m/hr or more planned for future flotation tanks, bubble size will have to be increased by a factor of two over the size currently employed in many facilities during dissolved air flotation.

A demonstration scaling-up of the dissolved air flotation

Dissolved air flotation (DAF) is currently being received in much attention as an effective process for solid–liquid separation in water technology. In this study, we scaled-up the DAF plant from a pilot-scale (72 m 3/day) to a full-scale (6000 m 3/day) plant and the sand-float type DAF was used. The concept of maintaining equal surface loading rate into scaling-up of DAF was a proper practice and strategy. In order to optimize the DAF plant, it was needed to determine the surface loading rate and air dissolving tube pressure. The optimum conditions of surface loading rate and air dissolving tube pressure were indicated in 7.5 m 3/m 2 day and 440 kPa from the pilot plant, respectively. The removal efficiency for TOC and UV 254 from the full-scale plant was as satisfactory as those from the pilot plant for the same surface loading rates. However, especially in flotation zone, the full-scale plant performed a little bit poorer than the pilot-scale plant in turbidity and chlorophyll- a reduction: because full-scale plant had long retention time and turbulent mixing condition during backwashing time which might be brought about the breakage of fragile flocs. Performance comparisons between the full-scale DAF plant and the conventional plant located at the city of Nam-Yang Ju in Korea are presented. DAF process showed higher efficiency than the conventional settling system improving the water quality in general, namely, turbidity, TOC, UV 254, Fe and Mn. We, therefore, conclude that DAF system should have substantial advantages over the conventional settling process in drinking water treatment.

Upgrading of Secondary Clarifiers by Inclined Plate Settlers

Secondary sedimentation is one of the most commonly used unit operations in wastewater treatment plants. It is customarily designed to achieve solids separation from biologically treated effluent through clarification of biological solids and thickening of sludge. As treatment plants receive increasingly high wastewater flow, conventional sedimentation tanks suffer from overloading problems which result in poor performance. Inclined plate settlers, a form of tube settlers, may have good potential in upgrading sedimentation tanks. This study was conducted to examine the possibility of applying inclined plate settlers in secondary sedimentation in order to upgrade conventional rectangular sedimentation tanks and improve their performance. Experiments were carried out at Al-Awir sewage treatment plant in Dubai using a pilot-scale inclined plate settler which received a mixed liquor stream from the high-rate activated sludge aeration tank. The results showed that inclined plate settlers perform slightly better than conventional type settlers during normal operation of plants, but during peak flows the inclined plate settlers showed much better performance than conventional settlers. The inclined plate settlers are less affected by overloading in comparison to conventional settlers. The solids removal efficiency increased as the hydraulic residence time was increased or as the surface loading rate was decreased. Application of these plates will not cause any interruption of daily operation of treatment plants and could be achieved at minimal cost when compared with other methods such as addition of chemicals, application of deep tanks, … etc. The study revealed that SS is a better parameter than TS, BOD, COD to evaluate the performance of sedimentation tanks. A statistical model was formulated to describe tank performance and design parameters were obtained based on the experimental results.

Factors affecting lead and cadmium levels in house dust in industrial areas of eastern Germany

The indoor exposure of 381 women (52–59 years old) to lead and cadmium was assessed by measuring the levels of the contaminants in sedimented house dust. The study was conducted in the areas surrounding the towns of Hettstedt, a region of mining and smelting of non-ferrous ores, of Bitterfeld, a centre of chemical production and coal mining, and of Zerbst, a primarily agricultural area. Factors that were significantly associated with lead and cadmium surface loading rates included the city area of residence, urban environment of dwelling, ventilation behaviour, type of heating, year of construction of building and crowding in the sampling room. In metal-contaminated areas, the transport of heavy metals into the home from external sources and their subsequent resuspension into the air due to normal household activities are significant factors in the exposure to heavy metals, whereas in unpolluted areas indoor sources play the major role.

Factors Affecting Lead, Cadmium, and Arsenic Levels in House Dust in a Smelter Town in Eastern Germany

Hettstedt, a city in eastern Germany with a long history of mining and smelting of nonferrous ores, has several industrial sources of heavy metals. The indoor exposure to metals of children (5 to 14 years old) in the Hettstedt area was assessed by measuring the levels of lead, cadmium, and arsenic contamination in sedimented house dust. Factors which influence the dust loading rate and the surface loading rates of these contaminants in house dust were investigated. The geometric mean of the dust loading rate was 8.9 mg/m2 day. The geometric means of surface loading rates were 1.14, 0.024, and 0.023 μg/m2 day for lead, cadmium, and arsenic, respectively. Factors that were significantly associated with surface loading rates included the city area of residence, automobile traffic near home, parent with occupational exposure to heavy metals, type of heating, housing characteristics, whether child's home is damp, number of persons living in the child's home, and parents' education. The most significant of these factors was the city area of residence, which reflects the distance from the metal sources; this factor accounted for about half of the variances explained by the regression models.

Upgrading of secondary clarifiers by inclined plate settlers

Secondary sedimentation is one of the most commonly used unit operations in wastewater treatment plants. It is customarily designed to achieve solids separation from biologically treated effluent through clarification of biological solids and thickening of sludge. As treatment plants receive increasingly high wastewater flow, conventional sedimentation tanks suffer from overloading problems which result in poor performance. Inclined plate settlers, a form of tube settlers, may have good potential in upgrading sedimentation tanks. This study was conducted to examine the possibility of applying inclined plate settlers in secondary sedimentation in order to upgrade conventional rectangular sedimentation tanks and improve their performance. Experiments were carried out at Al-Awir sewage treatment plant in Dubai using a pilot-scale inclined plate settler which received a mixed liquor stream from the high-rate activated sludge aeration tank. The results showed that inclined plate settlers perform slightly better than conventional type settlers during normal operation of plants, but during peak flows the inclined plate settlers showed much better performance than conventional settlers. The inclined plate settlers are less affected by overloading in comparison to conventional settlers. The solids removal efficiency increased as the hydraulic residence time was increased or as the surface loading rate was decreased. Application of these plates will not cause any interruption of daily operation of treatment plants and could be achieved at minimal cost when compared with other methods such as addition of chemicals, application of deep tanks, … etc. The study revealed that SS is a better parameter than TS, BOD, COD to evaluate the performance of sedimentation tanks. A statistical model was formulated to describe tank performance and design parameters were obtained based on the experimental results.

Enhanced transport of bacteria through a soil matrix using colloidal gas aphron suspensions

The influence of an anionic surfactant sodium dodecylbenzene sulfonate (DDBS) in the form of either an aqueous solution or microgas dispersion known as colloidal gas aphron (CGA) on the transport of a Psendomonas psendoalcaligenes, strain through a saturated soil matrix was examined. The experiments were conducted in 30‐cm‐long and 6.35 cm internal diameter stainless steel columns packed with a sandy clay loam. A 10‐ml pulse (0.033 pore volumes) of a bacterial suspension containing 1010 colony forming units (cfu) per ml was injected, and the column was eluted with either deionized water, a solution of DDBS, or a CGA suspension at a surface loading rate of 0.16 cm/min. The bacterial distributions within the column were similar after the passage of the water and surfactant solutions; however, the distribution of bacteria in the columns and effluent after the passage of the CGA suspension was markedly enhanced. The bacterial concentration in the lower half of the column after the passage of the CGA suspension was 2 to 3 orders of magnitude higher than that observed for either the surfactant or water solutions under similar experimental conditions. The final bacterial density in the effluent after the passage of the surfactant solution was one‐half order of magnitude greater than that in the effluent produced by passage of water. After the passage of the CGA suspension, the total number of bacteria in the effluent was at least 2 or 3 orders of magnitude greater than that obtained by passage of either surfactant or water as the eluting agent, respectively. The results of the study suggests that CGA suspensions can transport bacteria more efficiently than conventional surfactant solutions or water.

Simultaneous Biodegradation of 2,4-Dinitrotoluene and 2,6-Dinitrotoluene in an Aerobic Fluidized-Bed Biofilm Reactor

Mixtures of 2,4- and 2,6-dinitrotoluene are produced in large quantities as precursors of polyurethane foams and the explosive 2,4,6-trinitrotoluene (TNT). The two isomers are widely distributed in contaminated groundwater and soil. Bacteria capable of growing with the individual isomers as the sole source of carbon, nitrogen, and energy have been isolated previously. However, attempts to degrade 2,4- and 2,6-DNT simultaneously have failed. We tested the hypothesis that a mixed culture could degrade an isomeric DNT mixture if the bacteria were grown in an aerobic biofilm at low substrate concentrations. Such conditions were achieved with a fluidized-bed biofilm reactor (FBBR). The reactor was fed aqueous solutions containing 2,4- (40 mg L-1) and 2,6-DNT (10 mg L-1). The feed flow rate was gradually increased to yield surface loading rates of 36−600 mg of DNT m-2 d-1. Removal efficiencies higher than 98% for 2,4-DNT and 94% for 2,6-DNT were achieved at all loading rates. The nitrogen released from DNT was ...